Organic Chemistry Flashcards
(105 cards)
1
Q
What does structural formula mean?
A
It shows the arrangement of atoms in a molecule without showing every bond.
2
Q
What is a functional group?
A
A group of atoms responsible for characteristic reactions of a compound.
3
Q
Give the prefixes for
a. CH3 group
b. C2H5 group
c. Cl group
A
Methyl
Ethyl
Chloro
4
Q
Define structural isomerism?
A
When molecules have the same molecular formula but different structural formula.
5
Q
What are the 3 ways in which structural isomers can be formed?
A
- Alkyl groups can be in different places
- Functional groups can be bonded to different parts.
- There can be different functional groups.
6
Q
What are stereoisomers?
A
Organic compounds with the same molecular and structural formula but have different arrangement of atoms in space.
7
Q
What is E-Z isomerism and how are they decided?
A
E-Z isomerism is caused by limited rotation about the C=C double bonds.
If two substituents with the highest molecular mass are on the same side of the double bond it is Z isomer.
If they are on different sides it is the E isomer.
8
Q
What is homolytic fission?
A
Each atom gets one electron from the covalent bond.
It forms 2 free radicals
9
Q
What is heterolytic bond fission?
A
The bonding pair of electrons leave with one of the fragments and usually leads to ion formation.
-one atom gets both electrons
10
Q
What is a radical?
A
A species with an unpaired electron. Highly reactive.
11
Q
How is a covalent bond formed from two radicals?
A
The radicals collide and the electrons are involved in the bond formation.
12
Q
Describe the process of fractional distillation of crude oil?
A
- The oil is pre-heated then passed into a column.
- The fractions condense at different heights and the temperature of column decreases upwards.
- The separation of the rules depends on boiling point which depends in size of molecules. The larger the molecules the larger the London forces.
- Similar molecules condense together and so are collected at the same fraction.
- Small molecules condense at the top at lower temperatures and big molecules at the bottom at higher temperatures.
13
Q
What is cracking?
A
Cracking is the process of converting longer chain hydrocarbons into shorter chains. It is done by passing the hydrocarbons in the heavier fraction through a heated catalyst. This causes larger molecules to break up into smaller ones.
14
Q
What is structural isomerism?
A
Structural isomerism occurs when two or more compounds have the same formula but different structural formula.
15
Q
Define homologous series?
A
A family compound with the same functional group which differ in formula by CH2 from the next member.
16
Q
What’s an use of chain isomerism in the petrochemical industry?
A
Is is used to produce more branched alkanes with a higher octane number,from linear alkanes for fuels more suitable for petrol engines.
17
Q
What is an alkyl group?
A
A saturated section of a molecule derived from an alkane.
18
Q
Explain the use of arrows in mechanisms?
A
A half arrow head mean movement of a single electron, whilst a full arrow head shows an electron pair movement
19
Q
Explain in detail the process of fractional distillation?
A
- Crude oil is heated in a furnace which turns most of it into vapour, which is then passed into the column near the bottom.
- There is a temperature gradient in the column: it is hotter near the bottom and cooler near the top.
- Nearer the bottom of the column the fractions contain larger molecules with longer chains that have a higher boiling temperature.
- Nearer the top of the column the fraction contain smaller molecules with shorter chain and lower boiling points.
- Some of the hydrocarbons in crude oil are dissolved gases and they rise to the top of the column without condensing.
20
Q
What is crude oil?
A
-mixture of hydrocarbons
It is a finite resource found in rocks - its non-renewable and will run out eventually.
It is the remains of an ancient aquatic biomass consisting mainly of plankton.
21
Q
What is cracking and why do we do it?
A
As the world has fewer uses for shorter chain hydrocarbons there is a surplus of these. The demand for shorter chain hydrocarbons is much higher because they are better fuels and can be used to make other substance such as polymers.
Cracking is the process in which we convert the longer chains into shorter chains.
22
Q
Explain the process of Cracking ?
A
Cracking is the breakdown of molecules into shorter ones by heating with a catalyst.
- You pass the hydrocarbon in the heavier fractions through a heated catalyst (zeolite-made up Al,Si and O).
- This causes larger molecules to break up into smaller ones. From one large molecule two smaller molecules are formed
23
Q
Explain the process of reforming ?
A
Reforming is the conversion of straight chain hydrocarbons into branched chain and cyclic hydrocarbons by heating them with a catalyst,usually platinum.
24
Q
What is complete combustion in terms of fuels?
A
All the atoms in the fuel are fully oxidised.
25
What is incomplete combustion in terms of fuel?
It means that some of the atoms in the fuel are not fully oxidised.
26
How are oxides of sulphur formed during the combustion of alkane fuels?
Some of the molecules in the crude oil contain atoms of sulfur and these may not be removed by the fractional distillation,cracking or reforming process.
During the combustion of alkanes these atoms of sulfur from sulfur dioxide and then react in the air to form sulfur trioxide.
27
What are some of the problems that arise due to Oxides of sulfur being formed?
Both oxides are acidic. So when they dissolve in water in the atmosphere they form sulphurous acid and sulfuric acid.
Both these acids contribute to the formation of acid rain.
This causes damage to aquatic life in rivers and lakes and damage to crops and forests.
28
Explain the problems arising due to the formation of carbon monoxide?
Carbon monoxide is a toxic gas. In the body it prevents the transport of oxygen around the body.
29
How are oxides of nitrogen formed during the combustion of Alkane fuels?
Combustion of alkane fuels that contain nitrogen atoms occurs at very high temperatures. These condition cause nitrogen molecules in the air to react with oxygen molecules. These reactions lead to the formation of what are collectively known as oxides of nitrogen.
30
What are the problems arising due to the formation of oxides of nitrogen from combustion?
Nitrogen dioxide is acidic and can dissolve in water in the atmosphere forming nitrous acid and nitric acid. Both of these acids contribute to environmental damage by damaging aquatic life and damaging agriculture.
31
Explain how catalytic converters work solve some of the problem caused by pollutants?
Catalytic converters are fitted into the exhaust system of cars.
They have a ceramic honeycomb coated with a thin layer of catalyst metals (platinum, palladium and rhodium) - to give a large surface area.
As the exhaust gases from the engine pass through the converter they are turned into less harmful gases.(CO,NOx and unburned hydrocarbons to CO2,N2 and H20)
32
Why is there a need for alternative fuels?
1. over relying on fossil fuels and the problems of that
2. The depletion of natural resources
3. Global warming and climate change
33
What are some advantages of using biofuels?
1. Reduction of use of fossil fuels which are finite resources
2. biofuels are renewable
3. Use of biodiesel is more carbon-neutral.
4. No risk of large scale pollution from exploitation of fossil fuels.
34
Definition of a biofuel?
Any fuel that is derived from biomass - that is plant or algae or animal waste.
35
Disadvantages of biofuels?
1. Less food crops may be grown
2. rain forests have to be cut down to provide land
3. Shortage of fertile soils
36
Explain the properties of a C=C bond?
C=C double covalent bond consists of one sigma bond and one pi bond.
Pi bonds are exposed and have high electron density. They are therefore vulnerable to attack by species (electrophiles)
37
How is a sigma bond formed?
The overlapping of 2 s orbitals, or 1 s orbital and 1 p orbital or 2 p orbitals.
38
How is a pi bond formed?
The pi bond is formed by sideways overlap of two p orbitals on each carbon atom forming a pi bond above and below the plane of molecule.
39
How is margarine manufactured?
Hydrogenation.
Naturally occurring vegetable oils are unsaturated and so contain C=C double bonds. When these react with hydrogen, some of the C=C double bonds become C-C single bonds. This process changes the properties of the vegetable oil and converts it into a solid: which is margarine.
40
Explain the reaction of an alkene with halogens? (Conditions,reagent etc)
```
Alkene ——> dihalogenoalkane
Reagent - bromine (dissolved in organic solvent)
Conditions - room temperature
Mechanism - electrophilic addition
Type of bond fission - heterolytic
```
41
Explain the reaction of alkene with Halogen halides ? (Details)
```
Alkene —-> halogenoalkane
Reagent - HCl or HBr
Conditions - room temperature
Mechanism - electrophilic addition
Type of bond fission : heterolytic
```
42
What is a carbocation?
It is a positive ion in which the charge is shown on a carbon atom
43
What happens if the alkene is unsymmetrical in the addition of a hydrogen halides ?
The reaction will lead to 2 isomeric products.
| In electrophilic addition to alkanes the major product is formed via the more stable carbocation intermediate.
44
Why is the carbonation intermediate more stable?
The carbocation intermediate is more stable because the methyl groups on either side of the positive carbon are electron releasing and reduce the charge on the ion which stabilises it.
45
What reaction is used as a test for alkenes? What are the observations?
The raction of alkene with bromine water.
| orange colour of bromine water will decoulorise to colourles.
46
What is hydration?
involes the addition of water or steam
47
how are alcohols fromed from the hydration of alkenes? what are the essential conditions?
industrially alkenes are reacted with water in the presence of a acid catalyst (concentrated H3PO4).
- A high temperature
- A high pressure
48
why is the hydration alkenes to form alcohols preferred?
there are no waste products and so has a high atom economy. it also means seperation of products is easier and cheaper to carry out.
49
what is recycling?
recycling involves converting polymer waste into other materials.
50
uses of polyethene?
plastic bags, buckets, bottles. it is flexible easily moudle waterproof, chemical proof and low density plastic.
51
uses of polypropene?
its a stiffer polymer, used in utensils and containers and fibres in rope and carpets.
52
explain the process of recycling?
- sorting,as there are many types of polymer in use and these cannot be effectively processed together.
- processing this involves chopping the waste into small pieces and washing it. This material is then used to make new such materials,using methods such as melting, moulding and fibre production.
53
advanatges and disadavatnges of recycling?
adv- saves raw materials
dis- polymers need collecting, they can only be recycled into the same type.
thermoplastic polymers can be melted down and reshaped
54
what is incineration?
an incinerator takes in polymer waste and converts it into heat energy that can be used to heat homes and factories, or used to generate electricity.
55
what are the advantages and disadvatanges of incineration?
Dis- some toxins can be released on incineration. modern incinerator can burn more efficienty and most toxins and pollutants can be removed.
Adv - volume of rubbish is greatly reduced
56
what are biodegradeable polymers?
is one that can be broken down by microbes
57
how have chemists designed a way to remove waste gases from the incineration?
the waste gases from the incinerator are reacted with a base or carbonate. the base reacts with the acidic HCl gas, neutralising it.
58
define a nucleophile?
a nucleophile is a species that donates a loner pair of electrons to form a covalent bond with an electron-deficient atom.
59
what is hydrolysis?
reaction in which water or hydroxide ions replace an atom in a molecule with an -OH group.
-breaking using water
60
what makes halogenolkanes reactive?
as the halogen atom has a higher electronegatvity than carbon the C-X bond is polar. The carbon atom joined to the halogen is always slighty positive or the elctron-deficient part of the molecule, this makes it reactive
61
state and explain the trend in the rate of hydrolysis reaction of halogenalkanes?
the weaker the bond the easier it is to break and the faster the reaction.
iodoalkanes are the fastest to substiute (the precipitate is formed quicker) and are therefore the most reactive.
Fluorlalkanes are very unreactive due to the strength of the C-F bond.
62
name the colours of the precipitate formed during hydrolysis of halogenalkanes?
iodine - yellow
bromine - cream
chlorine - white
63
explain the reaction of halogenalkanes with aqeous potassium hydroxide to produce alcohols?
reagent- potassium hydroxide
conditions- in aqueous solution; heat under reflux
mechanism - nucleophilic substitution
the OH- is a stronger nucelophile than water as it has a full negstive charge and so is more strongly attracted to the Carbon +
64
why is it important to have aqueous conditions in the nucleophilic substitution reaction with hydroxide ions?
if the solvent were changed to ethanol an elimination reaction occurs.
65
why do we use excess ammonia in the production of primary amines from halogenalalkanes?
further substitution can occur between the haloalkane and the amines formed leading to a lower yield of the amine. using excess ammonia helps minimise this
66
what are nitriles?
organic compounds containing C-CN group.
67
Whats nucleophilic substitution?
a reaction in which an attacking nucelophile replaces an existing atom or group in a molecule.
68
What are some of uses of halogenoalkanes?
refrigerants, fire retardants, pesticides and aerosel propellants.
some halogenoalkanes have low flammability
69
what are some disadvantages of using halogenoalkanes?
halogenoalkanes are toxic and have detrimental effect on the ozone layer.
70
what are the bond angles in Alcohols?
the H-O-C bond is 104.5, because there are 2 bond pair of electrons and 2 lone pairs repelling to a position of minimum replusion. lone pairs repel more than bond pairs so the bond angle is reduced.
The H-C-H and C-C-O are 109.5 as there are 4 bond pairs of electrons repelling to a position of minimum repulsion.
71
What's the test used to distinguish between aldehydes and Ketones?
Fehling's (Benedict's) solution.
reagent - fehling's solution containing Cu 2+ ions.
reaction - aldehydes only are oxidised by Fehling's solution into a carboxylic acid and the copper ions are reduced copper (I) oxide.
Observation - Aldehydes: Blue Cu 2+ ions in solution change to a red precipitate of Cu2O.
ketones do not react.
72
How can you test for the presence of a carboxylic acid?
the presence of a carboxylic acid can be tested by the addition of sodium carbonate. it will fizz and produce carbon dioxide.
73
why do we use anti-bumping granules?
anti bumping granules are added to the flask in both distillation and reflux to prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles.
74
what is a diol?
compound containing two OH groups
75
what is use as a feedstock?
use as a feedstock involves converting polymer waste into chemicals that can be used to make new polymer
76
explain the nucleophilic substitution of halogenoalkanes with ammonia?
halogenalkane --> amine
reagent - NH3 dissolved in ethanol.
cond - heating under pressure in a sealed tube or else the ammonia would escape before it could react
type of reagent - nucleophile
77
explain the reaction of an halogenoalkane with potassium cyanide ?
R-X --> R-CN
heating a halogenoalkane with KCN dissolved in ethanol under reflux to make nitriles.
- the attacking nucleophile is a CN- ion.
- the organic product contains one more carbon atom than the starting material.
-it is a useful way to extend the carbon chain and an important way to synthesise more complex compounds.
78
explain what happens when you use ethanol instead of water as a solvent in the nucleophilic substitution?
When a halogenoalkane is heated with ethanolic potassium hydroxide, the OH- ion acts as a base and not a nucleophile.
79
Explain the reactions of Alcohols with soidum?
```
2CH3CH2OH + 2Na ---> 2CH3CH2O-Na+ + H2.
- this reaction can be used as a test for alcohols.
observations
effervesence
the mixture gets hot
soidum dissolvs
white solid is produced.
```
80
explain the reaction of alcohols to halogenoalkanes?
- substituion
| - these reactions involve replacing the hydroxyl group in an alcohol molcule with a halogen atom.
81
explain the reaction of alcohols with phosphourous (V) chloride?
(chlorination)
CH3CH2OH + PCl5 --> CH3CH2Cl + POCl3 + HCl.
This reaction with PCl5
(phosphorous(V)chloride) can be used as a
test for alcohols. You would observe misty
fumes of HCl produced.
PCl5/ PCl3/ conc HCl / SOCl2
/ mixture of NaCl +
H2SO4 can all be uses for substituting a Cl.
82
Explain the bromination reaction to alcohols?
CH3CH2OH + HBr --> CH3CH2Br + H2O.
For Br use KBr, 50% concentrated H2SO4
to produce HBr.
83
explain the reaction of dehydration of alcohols to alkenes?
-this is done by heating the alcohol with concentrated phosphoric acid.
this reaction is similar to the elimination reaction of a halogenoalkane, with he OH group and a hydrogen atom from an adjacent carbon being removed and a C=C double formed in the carbon chain.
its called DEHYDRATION as water is the only inorganic product.
-elimination
-
84
What is the oxidsing agent that causes alcohols to oxidise?
potassium dichromate
85
explain the reaction of partial oxidation of primary alcohols?
primary alcohol --> aldehyde
reagent- potassium dichromate (VI) solution and dilute sulfuric acid.
cond - (use a limited amount of dichromate) warm gently and distill out the aldehyde as it forms.
observation - the
orange dichromate ion
(Cr2O72-) reduces to
the green Cr 3+ ion
86
explain the reaction of full oxidation of primary alcohols?
primary alcohols --> carboylic acid
reagent- potassium dichromate (VI) solution and dilute sulfuric acid.
cond- use an excess of dichromate and heat under reflux (distill of product after the reaction has finished)
observation- the
orange dichromate ion
(Cr2O72-) reduces to
the green Cr 3+ ion.
87
explain the reaction of the oxidation of secondary alcohols?
secondary alcohol --> ketone
reagent - potassium dichromate (VI) solution and dilute sulfuric acid.
cond - heat under reflux.
observation - the orange dichromate ion (Cr2O72-) reduces to
the green Cr 3+ ion.
88
why can't tertiary alcohols be oxidised at all by potassium dichromate?
this is because there is no hydrogen atom bonded to the carbon with the OH group.
89
Whats the test for aldehydes?
-fehling's solution containing Cu 2+ ions.
cond - heat gently
reaction - aldehydes only are oxidised by fehling's solution into a carboxylic acid and the copper (II) ions are reduced to copper (I) ions.
observation - blue solution to red precipitate.
90
what are the techniques used to purify an organic liquid?
- simple distillation
- fractional distillation
- solvent extraction
- drying
91
explain the process of simple distillation?
- distillation of an impure liquid invovles heating it in a flask connected to a condenser.
- the liquid with the lowest boiling temperature evaporates off first and passes into the condenser first. this means it can be collected in the reciever separately from any other liquid that evaporates later.
- thermometer is used to monitor the temperature of the vapour as it passes into the condenser. if the temperature remains steady,this indicates that one compound is distilling over. if the temperature begins to rise, this indicates that a different compound is distilling over
92
which halogenoalkanes have the fastest rate of reaction?
tertiary halogenoalkanes are more rapidly hydrolysed than secondary and primary compounds.
93
advantages and disadvantages of simple distillation?
- easier and quicker to set up
| - disadvanatges is that it does not seprate liquids as well as fractional distillation.
94
explain what is fractional distillation?
- same apparatus as simple distillation, but with a fractionating column between the heating flask and the still head.
- th column is filled with glass beads which act as surfaces on which the vapour leaving the column can condense and then be evaporated again as more hot vapour passes up the column.
95
advanatges and disadvantages of fractional distillation?
adv - several compounds can be seperated froma mixture.
the vapour undergoes repeated distillations as it passes up the column which provides better seperation.
dis - longer
96
what is solvent etraction?
method is used to seperate a liquid from a mixture by causing it to move from the mixture to the solvent.
97
what factors decide what solvent should be used for solvent extraction?
- the solvent added should be immiscible with the solvent containing the desired organic product.
- the desired organic product should be much more souble in the solvent added than in the reaction mixture.
98
explain the technique of drying with anyhdrous salts?
- the drying agent is added to the organic liquid and the mixture is swirled and then left for a period of time.
- before use the drying agent is powdery but after absorbing water it looks more crystaline.
- if a bit more drying agent is added and it remains powedery, this is an indication that the liquid is dry.
- the drying agent is removed either by decantation (pouring the organic liquid off the solid dryig agent) or by filtration.
99
test for purities for liquids?
measure its boiling temperature, impurities raise the boiling temperature
100
test for carboxylic acid?
- add sodium carbonate
| - effervescence of CO2 evolved.
101
test for chloroalkane?
- warm with silver nitrate
- add mixture of water and ethanol
- slow formation of white precipitate of AgCl
102
test for Acyl chloride?
- silver nitrate
| - vigorous reaction - steamy fumes of HCl -r rapid white precipitate of AgCl
103
Why can’t ketones be further oxidised into carboxylic acid?
-there are no C-H bond into which an oxygen atom can be inserted.
104
Why are tertiary alcohols not readily oxidised?
- they do not have available H atoms to give up.
105
Test for alcohols?
1)Reaction with PCl5 can be used.
Observe Misty fumes of HCl produced.
2)reaction with sodium
-observation- effervescence, mixture gets hot, sodium dissolves
White solid is produced.
